March 25, 2013

Update 4/2/2013: in an email to the IETF JSON mailing list, Barry Leiba (Applications Area director in IETF) noted that discussions had started with ECMA and ECMA TC 39 to reach agreement on where JSON will be standardized, before continuing with the chartering of an IETF working group.

JSON (JavaScript Object Notation) is a text representation for data interchange. It is derived from the JavaScript scripting language for representing data structures and arrays. Although derived from JavaScript, it is language-independent, with parsers available for many programming languages.

JSON is often used for serializing and transmitting structured data over a network connection. It is commonly used to transmit data between a server and web application, serving as an alternative to XML.

JSON was originally specified by Doug Crockford in RFC 4627, an "Informational" RFC. IETF specifications known as RFCs come in lots of flavors: an "Informational" RFC isn't a standard that has gone through careful review, while a "standards track" RFC is.

An increasing number of other IETF documents want to specify a reference to JSON, and the IETF rules generally require references to other documents that are the same or higher levels of stability. For this reason and a few others, the IETF is starting a JSON working group (mailing list) to update RFC 4627.

The JavaScript language itself is standardized by a different committee (TC-39) in a different standards organization (ECMA). For various reasons, the standard is called "ECMAScript" rather than JavaScript. TC 39 published ECMAScript 5.1, and are working on ECMAScript 6, with a plan to be done in the same time frame as the IETF work.

The W3C also is developing standards that use JSON and need a stable specification.

Risk of divergence

Unfortunately, there is a possibility of (minor) divergence between the two specifications without coordination, either formally (organizational liaison) or informally, e.g., by making sure there are participants who work in both committees.

Having multiple conflicting specifications for JSON would be bad. While some want to avoid the overhead of a formal liaison, there needs to be explicit assignment of responsibility. I'm in favor of a formal liaison as well as informal coordination. I think it makes sense for IETF to specify the "normative" definition of JSON, while ECMA TC-39's ECMAScript 6.0 and W3C specs should all point to the new IETF spec.

JSON vs. XML

JSON is often considered as an alternative to XML as a way of passing language-independent data structures as part of network protocols.

In the IETF, BCP 70 (also known as RFC 3470) "Guidelines for the Use of Extensible Markup Language (XML) within IETF Protocols" gives guidelines for use of XML in network protocols. However, this published in 2003. (I was a co-author with Marshall Rose and Scott Hollenbeck.)

But of course these guidelines don't answer the question many have: When people want to pass data structures between applications in network protocols, do they use XML or JSON and when? What is the rough consensus of the community? Is it a choice? What are the alternatives and considerations? (Fashion? deployment? expressiveness? extensibility?)

This is a critical bit of web architecture that needs attention. The community needs guidelines for understanding the competing benefits and costs of XML vs. JSON. If there's interest, I'd like to see an update to BCP 70 which covers JSON as well as XML.